- 1 cup whipping cream
- 1/2 cup sour cream
- 3 teaspoons minced peeled fresh ginger
- 1 1/2 teaspoons grated orange peel
- 10 tablespoons (1 1/4 sticks) butter
- 3 1/2 pounds red-skinned sweet potatoes (yams), peeled, cut into 1/2-inch pieces
- 1 tablespoon golden brown sugar
- 2 large leeks, chopped (white and pale green parts only)
- 1 1/3 cups finely chopped celery
- 10 cups (or more) canned low-salt chicken broth
- 1 1/3 cups orange juice
- 3 1-pound cooked lobster tails
- 2 tablespoons chopped fresh parsley
- Mix cream, sour cream, 1 1/2 teaspoons ginger and orange peel in medium bowl to blend. Let stand until thickened, about 3 hours. Cover crème fraîche and refrigerate.
- Preheat oven to 400°F. Melt 4 tablespoons butter in large pot over medium heat. Remove from heat. Add sweet potatoes and sugar and toss to coat. Arrange sweet potatoes on 2 baking sheets. Roast until very tender and starting to brown, stirring occasionally, about 30 minutes.
- Melt 4 tablespoons butter in same pot over medium heat. Add leeks, celery and remaining 1 1/2 teaspoons ginger and sauté until leeks begin to soften, about 5 minutes. Add roasted sweet potatoes and sauté 2 minutes. Add 10 cups broth and orange juice. Bring mixture to boil. Reduce heat and simmer until leeks and celery are very tender, about 20 minutes.
- Working in batches, puree soup in processor. Return soup to pot. Thin with more broth, if desired. Season with salt and pepper. (Crème fraîche and soup can be made 2 days ahead. Cover separately; chill.)
- Remove lobster meat from shells. Slice into 1/3-inch-thick medallions. Melt 2 tablespoons butter in heavy large skillet over medium heat. Add lobster; sauté until heated through, about 1 minute.
- Bring soup to simmer. Ladle into bowls. Spoon small dollops of crème fraîche atop soup. Draw skewer through crème fraîche to form design. Arrange lobster atop soup. Sprinkle with parsley.